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	<div id="winchm_template_button"><A href="loading_debugger_extension_dlls.htm" title="Previous topic"><img id="winchm_template_prev" alt="Previous topic" src="../template2/btn_prev_n.gif" border="0"></a><A href="writing_new_debugger_extensions.htm" title="Next topic"><img id="winchm_template_next" alt="Next topic" src="../template2/btn_next_n.gif" border="0"></a></div>
	<div id="winchm_template_navigation">Help &gt; 
<A href="introduction6.htm">Debugging Tools for Windows (WinDbg, KD, CDB, NTSD)</A> &gt; <A href="debugger_operation_win8.htm">Debugger Operation</A> &gt; <A href="debugger_extensions.htm">Using Debugger Extensions</A> &gt; </div>
	<div id="winchm_template_title">Using Debugger Extension Commands</div>
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	<div id="winchm_template_content"><div id="mainSection"><p>The use of debugger extension commands is very similar to the use of <a href="#Bookmark1265">debugger commands</a>. The command is typed in the Debugger Command window, producing either output in this window or a change in the target application or target computer.</p>
<p>An actual debugger extension command is an entry point in a DLL called by the debugger.</p>
<p>Debugger extensions are invoked by the following syntax:</p>
<p><b>![</b><i>module</i><b>.]</b><i>extension</i><b> [</b><i>arguments</i><b>]</b></p>
<p>The module name should not be followed with the .dll file name extension. If <i>module</i> includes a full path, the default string size limit is 255 characters.</p>
<p>If the module has not already been loaded, it will be loaded into the debugger using a call to <b>LoadLibrary</b>(<i>module</i>). After the debugger has loaded the extension library, it calls the <b>GetProcAddress</b> function to locate the extension name in the extension module. The extension name is case-sensitive and must be entered exactly as it appears in the extension module's .def file. If the extension address is found, the extension is called.</p>
<h3><a id="search_order"></a><a id="SEARCH_ORDER"></a>Search Order</h3>
<p>If the module name is not specified, the debugger will search the loaded extension modules for this export.</p>
<p>The default search order is as follows:</p>
<ol>
<li>
<p>The extension modules that work with all operating systems and in both modes: Dbghelp.dll and winext\ext.dll.</p>
</li>
<li>
<p>The extension module that works in all modes but is operating-system-specific. For Windows XP and later versions of Windows, this is winxp\exts.dll. There is no corresponding module for Windows 2000.</p>
</li>
<li>
<p>The extension module that works with all operating systems but is mode-specific. For kernel mode, this is winext\kext.dll. For user mode, this is winext\uext.dll.</p>
</li>
<li>
<p>The extension module that is both operating-system-specific and mode-specific. The following table specifies this module.<table>
<tr>
<th>Windows Build</th>
<th>User Mode</th>
<th>Kernel Mode</th>
</tr>
<tr>
<td>
<p>Windows 2000 (free build)</p>
</td>
<td>
<p>w2kfre \ ntsdexts.dll</p>
</td>
<td>
<p>w2kfre \ kdextx86.dll</p>
</td>
</tr>
<tr>
<td>
<p>Windows 2000 (checked build)</p>
</td>
<td>
<p>w2kchk \ ntsdexts.dll</p>
</td>
<td>
<p>w2kchk \ kdextx86.dll</p>
</td>
</tr>
<tr>
<td>
<p>Windows XP and later</p>
</td>
<td>
<p>winxp \ ntsdexts.dll</p>
</td>
<td>
<p>winxp \ kdexts.dll</p>
</td>
</tr>
</table>
<p> </p>
</p>
</li>
</ol>
<p>When an extension module is unloaded, it is removed from the search chain. When an extension module is loaded, it is added to the beginning of the search order. The <a href="#Bookmark2179"><b>.setdll (Set Default Extension DLL)</b></a> command can be used to promote any module to the top of the search chain. By using this command repeatedly, you can completely control the search chain.</p>
<p>Use the <a href="#Bookmark2067"><b>.chain (List Debugger Extensions)</b></a> command to display a list of all loaded extension modules in their current search order.</p>
<p>If you attempt to execute an extension command that is not in any of the loaded extension modules, you will get an Export Not Found error message.</p></div></div>	
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